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Lesson · Grade 7 · Mathematics

Multiplying integers: the sign rules

  • Grade 7
  • Mathematics
  • 1 min 2 s
  • British Columbia
  • BC7-MA-11

Starting from 3 groups of −4, a table makes the first number 1 smaller on each row, and each answer goes up by 4 until it reaches −3 × (−4) = 12. The rows then show the rule: same signs give a positive answer and different signs give a negative one, which is applied to the same example (3 × 4 = 12, both signs negative, so positive 12).

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In one sentence

The question this lesson answers

What is negative 3 times negative 4?

Start with 3 times negative 4, which means 3 groups of negative 4.

Transcript

What the lesson says

What is negative 3 times negative 4?

Start with 3 times negative 4, which means 3 groups of negative 4.

Together, the 3 groups make negative 12.

Now make the first number 1 smaller each time.

Each answer is 4 more than the one above it.

Keep the pattern going past zero.

So negative 3 times negative 4 is positive 12.

When the two signs are the same, the answer is positive.

When the two signs are different, the answer is negative.

To use the rule, multiply the numbers, then choose the sign.

3 times 4 is 12.

Both signs are negative, so the answer is positive 12.

Remember: same signs give a positive answer, and different signs give a negative answer.

Curriculum

Where this fits

British Columbia, Grade 7

Mathematics, Number: operations with integersBC7-MA-11

Previous: Subtracting integers: add the oppositeNext: Why a Negative Times a Negative Is Positive

The outcomes and strands follow the British Columbia curriculum.

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